In an imaging device using a solid-state image sensing device of a digital still camera or the like, a near-infrared cut filter transmitting visible light but blocking infrared light is typically disposed in an optical path to the solid-state image sensing device, so as to make the sensitivity of the solid-state image sensing device close to the visibility of human.
As such a near-infrared cut filter, a filter is known in which an absorption layer containing a dye absorbing near-infrared light, and a reflection layer having stacked dielectric thin films with different refractive indexes to reflect and block near-infrared light by interference of light are combined. In this filter, a dielectric multilayer film constituting the reflection layer has optical film thicknesses of respective films which are different depending on an incident angle of light. Thus, there is a problem that it has incident angle dependence in its spectral characteristic, and that color reproducibility is different depending on the incident angle.
On the other hand, Patent Reference 1 (JP-B2 4169545) discloses a filter using a near-infrared absorbing glass in which CuO or the like is added to a fluorophosphate-based glass or a phosphate-based glass so as to enable selective absorption of near-infrared light. However, the incident angle dependence is recognized also in this filter, and the problem of different color reproducibility depending on the incident angle remains unsolved.
Further, Patent Reference 2 (JP-A 2008-051985) discloses a near-infrared cut filter including an absorption layer and a reflection layer constituted of a dielectric multilayer film, the filter having a spectral characteristic to exhibit high transmittance exceeding 90% in a visible wavelength range and exhibit low transmittance of 5% or less in an infrared wavelength range. In this filter, for example, the wavelength at which transmittance becomes 50% is in the vicinity of 650 nm, and the transmittance on a long wavelength side is high with reference to a relative visibility curve, having a problem that color reproducibility particularly of redness cannot be obtained with high accuracy.
Moreover, Patent Reference 3 (JP-A 2014-052482) similarly discloses a near-infrared cut filter including an absorption layer and a reflection layer constituted of a dielectric multilayer film. This filter has a spectral characteristic closer to the relative visibility curve on the long wavelength side than that disclosed in Patent Reference 2. However, the above-described incident angle dependence of the spectral characteristic of this filter is large, and there is still a problem that color reproducibility differs depending on the incident angle.